Illegal Marijuana Farms May Poison the Rare Fisher in California

Illegal pot farms may just be harming the rare, forest-dwelling fisher. Scientists have found that illegal marijuana farms in California are threatening this species.

Previous studies showed that rat poisons were present in the tissues of this cat-sized relative of the weasel family when they were in proximity of illegal marijuana cultivation sites. In this latest study, the researchers decided to look at these animals a bit more closely; they examined the deaths of 167 fishers-129 of which cause of death was determined.

So what did the researchers find? It turns out that Northern California fishers were five times more likely to die from poisoning than predation compared to fishers in the southern Sierra Nevada. In addition, male fishers were 13 times more likely to die of poisoning than predation compared to females. This is possibly due to the large movements made by males during the spring breeding seasons. Also, 85 percent of fishers showed exposure to rat poison, and poisoning accounted for 10 percent of all documented fisher mortalities.

"We know that a 10 percent change in mortality rate is enough to determine whether fishers in California are able to expand their population size or not," said Craig Thompson, one of the researchers, in a news release. "Now we know that rodenticide poisoning alone is enough to keep fisher populations suppressed in the state, even without accounting for the fact that low doses of these poisons also cause the animals to be lethargic and susceptible to disease, which in turn increases the potential for other sources of mortality."

The findings reveal that officials should remediate and remove these threats to fishers. By controlling the pot trade, it may be possible to institute farming regulations that will help save these animals.

The findings are published in the journal PLOS One.

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